FX489 Datasheet, PDF (5/12 Pages) List of Unclassifed Manufacturers – GMSK Modem

Application Information ......
Rx FREQUENCY
DISCRIMINATOR
SIGNAL AND
DC LEVEL
ADJUSTMENT
Rx SIGNAL IN
Rx FEEDBACK
RxD
MICRO RxC
CONTROLLER TxD
TxC
Rx DATA
Rx CLOCK
Tx DATA
Tx CLOCK
Rx
CIRCUITS
Tx
CIRCUITS
FX489
GMSK MODEM
FREQUENCY
MODULATOR
SIGNAL AND
DC LEVEL
ADJUSTMENT
Tx OUT
Fig.3 External Signal Paths
Clock Oscillator and Dividers
The Tx and (nominal) Rx data rates are determined
by division of the frequency present at the Xtal pin,
which may be generated by the on-chip Xtal oscillator
or be derived from an external source.
Note that device operation is not
guaranteed or specified above 19,200 bits/s
or below 4,000 bits/s.
ClkDiv ClkDiv
A
B
Division ratio
Xtal Freq/
Data Rate
0
0
128
0
1
256
1
0
512
1
1
1024
Table 1 Clock/Data Rates
4.096
[12.288/3]
16000
8000
4000
Radio Channel Requirements
To achieve legal adjacent channel performance at
high bit-rates, a radio with an accurate carrier
frequency and an accurate modulation index will be
4.9152MHz
RxD
SERIAL
RxC
I/O PORT TxD
TxC
MICROCONTROLLER
Fig.4 Minimum µController System Connections
The division ratio is controlled by the logic level
inputs on the ClkDivA/B pins, and is shown in the table
below - together with an indication of how various
‘standard’ data rates may be derived from common µP
Xtal frequencies.
Xtal/Clock Frequency (MHz)
4.9152
2.048
[6.144/3]
2.4576
[12.288/5]
Data Rate (bps)
19200
9600
4800
16000
8000
4000
19200
9600
4800
required.
To achieve optimum channel utilization, (eg. low
BER and high data-rates) attention must be paid to the
phase and frequency response of both the IF and
baseband circuitry.
SETTINGS: D/Rate 4800bps - BT 0.5 - Rx & Tx Enabled
XTAL/CLOCK
XTAL
V_DD
Tx ENABLE
Rx DATA
Rx CLOCK
Tx DATA
Tx CLOCK
PLLacq
RxDCacq
FX489
GMSK MODEM
ClkDIVA
ClkDIVB
BT
RxHOLD
Rx S/N
Tx PS
Rx PS
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